A pressure sensor device is typically mounted on a block, such as an oil enclosing block of a transmission of an automobile or an oil block of a hydraulic actuator, to measure pressure, and uses a semiconductor pressure sensor chip, applying a piezo-resistance effect as a sensor element. The semiconductor pressure sensor has an arrangement in which a plurality of semiconductor strain gauges, connected in a bridge circuit, are formed on a diaphragm made of a material, such as single crystal silicon, that exhibits a piezo-resistance effect. Deformation of the diaphragm by a pressure variation causes a variation corresponding to the amount of the deformation, in the gauge resistance of the semiconductor strain gauge. The amount of variation is output from the bridge circuit as a voltage signal.
FIGS. 16-19 illustrate some well known pressure sensor devices. The pressure sensor device shown in FIG. 16 is provided with a joint 1 having a threaded section, a flange member 3 for screwing the joint 1 into a section to which the device is installed. The pressure sensor 2 outputs a voltage signal corresponding to the amount of variation in pressure as explained above. It includes a circuit board 4 mounting a circuit chip for processing the output signal of the pressure sensor 2, a wire bonding 5 connecting the pressure sensor 2 and the circuit board 4, and terminals 6 and 7 for outputting the signal from the circuit board 4 to the outside. The terminal 6 and a terminal stand 8, which supports the terminal 7, are secured to the flange member 3 by a joint member 11. Moreover, a gasket 9 and an O-ring 10 are assembled onto the flange member 3, as shown in FIG. 1 of JP-A-2002-168718, for example.
The pressure sensor device shown in FIG. 17 is composed of a transducer 12, a hexagon port 13, a cover 14, an annular sealing gasket 15, a periphery clip 16, a flexible circuit 17, and a base member 18 for outputting a signal to the outside. The transducer 12 is composed of a first conductive film, which deforms on receiving pressure, a second conductive film facing the first conductive film with a spacer held between the two conductive films, and a circuit for converting electrostatic capacitance varied by the deformation of the first conductive film to a voltage signal, as shown in FIG. 1 of JP-A-2002-202215, for example.
The pressure sensor device shown in FIG. 18 has an arrangement in which, in a sensor case 24, a pressure sensor chip 25 is connected to connecting leads 19, 20, 21, and 22. The connecting leads 19, 20, 21, and 22 are secured to the sensor case 24 while being insulated from one another by a hermetically sealing glass 23. Along with this, the pressure sensor chip 25 is encapsulated in silicon oil covered with a metallic diaphragm 26, as shown in FIGS. 8 and 10 of JP-A-2000-55762, for example. The pressure sensor device is protected by a metallic hardcover 27 at the upper side of the device.
The pressure sensor device shown in FIG. 19 has an arrangement in which the pressure sensor device shown in FIG. 18 is contained in a metallic housing 28 using an O-ring 29. In the metallic housing 28, a connector housing 33, having terminal boards 30, 31, and 32 electrically connected to the connecting leads 19, 20, 21, and 22, is incorporated together with an O-ring 34 and a spacer ring 35 for securing thereto. Securing is carried out by bending part of the metallic housing 28 and engaging the bent part with the connector housing 33. The metallic housing 28 has a pressure receiving port 36, a threaded section 37, a fastening section 38, and a stepped portion 39. See JP-A-2000-55762, for example.
Moreover, it is known, in a semiconductor pressure sensor, to use a semiconductor element, having a diaphragm section with a set of piezo-resistors formed thereon and an amplifying circuit of an output signal from the set of piezo-resistors. The amplifying circuit is formed by integrating a combination of an operational amplifier and a resistance network, including thin film resistors. In a pressure sensor device using the semiconductor pressure sensor, the semiconductor pressure sensor is contained in a sealed container. In the container, the space on the side to which the surface of the semiconductor sensor faces is kept in a constant pressure. Thus, an arrangement is provided in which, with the pressure in the container taken as a reference, pressure applied onto the back of the semiconductor pressure sensor is measured, as disclosed in JP-A-1-150832, for example.
In the pressure sensor device shown in FIG. 16 or FIG. 17, however, numerous parts raise the material cost and the assembly cost. Moreover, in each of the devices, the signal transmission path is made up of numerous parts, which require numerous connections. In the device shown in FIG. 16, the signal transmission path includes the pressure sensor 2, the wire bonding 5, the circuit board 4, the circuit chip, the terminal 6, and the terminal 7. While, in the device shown in FIG. 17, the path includes the transducer 12, the flexible circuit 17, the circuit chip, and the base member 18. This increases the failure probability, which results in long-term reliability issues. Furthermore, in the device shown in FIG. 16, the direct joint of the joint 1 and the pressure sensor 2 can cause stress, which is produced when screwing the joint 1, and transmit it to the pressure sensor 2. This lowers the accuracy and reliability of the measured signal.
Moreover, in the pressure sensor device shown in FIG. 18, external noises applied to the leads affect the silicon oil to polarize, which sometimes causes electric charges to accumulate on the surface of the pressure sensor chip 25. This can vary the signal output from the pressure sensor chip 25 and lower the reliability of the measured signal. Furthermore, an increase in an inner pressure due to expansion of the silicon oil under a high temperature environment and compression of the silicon oil when applying a high pressure produces repeated stresses in the metallic diaphragm 26. This fatigues the metallic diaphragm 26, which is becomes problematic with the long-term reliability. In addition, in the pressure sensor device shown in FIG. 19, the large area of the section for receiving pressure results in a large applied load to the device. For supporting such a load, rigidity of the metallic housing 28 must be increased. This increases the cost and upsizes the device.
Moreover, in the pressure sensor device disclosed in JP-A-1-150832, since the external signal terminals for outputting the output signals to the outside are glass-sealed at the bottom of the container, it can be supposed that the container is made of metal. However, the metal container has the disadvantage of being expensive. Furthermore, the external signal terminals and a pressure introducing port are provided on the same side. Therefore, when the pressure sensor device is used for such a purpose as to measure the pressure while mounted to an oil-enclosing block or an actuator block, the external signal terminals interrupt the pressure sensor device to make it difficult to mount the pressure sensor device on the oil-enclosing block or the like. Therefore, the external signal terminals must be projected on the side opposite to the side on which the pressure introducing port is provided. However, as explained above, when the container is metallic, it is difficult to provide the external terminals on the opposite side of the pressure introducing port.
There still remains a need for a pressure sensor device that can be manufactured with a low cost, have a high long-term reliability, and with measured signals of high accuracy and reliability, and in particular with external terminals disposed on the opposite side of the pressure introducing port. The present invention addresses this need.